pytutorial/python_basics/list

Sequence Types: list

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* TOC {:toc}

The goal

Lists are mutable sequences, typically used to store collections of homogeneous items (where the precise degree of similarity will vary by application).​

Quote

Questions to David Rotermund

Example Lists

With homogeneous items:

primes = [2, 3, 5, 7]

collection_of_strings = [
    "AA",
    "BB",
    "CC",
    "DD",
    "EE",
    "FF",
    "GG",
    "HH",
]

A mixture of type:

def my_function(a):
    return a

my_favourite_things = [32, "sleep", my_function]

Indexing

collection_of_strings = [
    "AA",
    "BB",
    "CC",
    "DD",
    "EE",
    "FF",
    "GG",
    "HH",
]


print(collection_of_strings[0])  # -> AA
print(collection_of_strings[1])  # -> BB
print(collection_of_strings[-2])  # -> GG
print(collection_of_strings[-1])  # -> HH

Slicing

collection_of_strings = [
    "AA",
    "BB",
    "CC",
    "DD",
    "EE",
    "FF",
    "GG",
    "HH",
]


print(collection_of_strings[0:3])  # -> ['AA', 'BB', 'CC']
print(collection_of_strings[:3])  # -> ['AA', 'BB', 'CC']
print(collection_of_strings[3:])  # -> ['DD', 'EE', 'FF', 'GG', 'HH']
print(collection_of_strings[1:-1])  # -> ['BB', 'CC', 'DD', 'EE', 'FF', 'GG']
print(collection_of_strings[-3:])  # -> ['FF', 'GG', 'HH']

Changing lists

collection_of_strings = [
    "AA",
    "BB",
    "CC",
    "DD",
    "EE",
    "FF",
    "GG",
    "HH",
]

collection_of_strings[3] = "II"
print(collection_of_strings)  # -> ['AA', 'BB', 'CC', 'II', 'EE', 'FF', 'GG', 'HH']
collection_of_strings[:3] = ["JJ", "KK", "LL"]
print(collection_of_strings)  # -> ['JJ', 'KK', 'LL', 'II', 'EE', 'FF', 'GG', 'HH']
collection_of_strings[:4] = [
    "MM",
    "NN",
    "OO",
    "PP",
]
print(collection_of_strings)  # -> ['MM', 'NN', 'OO', 'PP', 'EE', 'FF', 'GG', 'HH']

List functions

len() and sorted()

collection_of_strings = [
    "GG",
    "HH",
    "AA",
    "BB",
    "EE",
    "FF",
    "CC",
    "DD",
]


print(len(collection_of_strings))  # -> 8
print(sorted(collection_of_strings)) # -> ['AA', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH']

max() and sum()

primes = [2, 3, 5, 7]
print(sum(primes)) # -> 17
print(max(primes)) # -> 7

append(), pop(), and remove()

collection_of_strings = [
    "AA",
    "BB",
    "BB",
    "CC",
    "DD",
    "EE",
    "FF",
    "GG",
    "HH",
]

collection_of_strings.append("II")
print(
    collection_of_strings
)  # -> ['AA', 'BB', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH', 'II']
print(collection_of_strings.pop())  # -> II
print(
    collection_of_strings
)  # -> ['AA', 'BB', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH']

collection_of_strings.remove("BB")
print(collection_of_strings)  # -> ['AA', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH']

collection_of_strings.remove("BB")
print(collection_of_strings)  # -> ['AA', 'BB', 'CC', 'DD', 'EE', 'FF', 'GG', 'HH']

collection_of_strings.remove("BB")
print(collection_of_strings)  # -> ValueError: list.remove(x): x not in list

Index

collection_of_strings = [
    "AA",
    "BB",
    "CC",
    "DD",
    "EE",
    "FF",
    "GG",
    "HH",
]

print(collection_of_strings.index("CC"))  # -> 2
print(collection_of_strings.index("XX"))  # -> ValueError: 'XX' is not in list

del and insert

collection_of_strings = []
collection_of_strings.append("BB")
collection_of_strings.append("CC")
collection_of_strings.append("DD")
print(collection_of_strings)  # -> ['BB', 'CC', 'DD']

collection_of_strings.insert(0, "AA")
print(collection_of_strings)  # -> ['AA', 'BB', 'CC', 'DD']

del collection_of_strings[1]
print(collection_of_strings)  # -> ['AA', 'CC', 'DD']